MIMO (Multiple-Input Multiple-Output) transmission is a method for transmitting data by radio using a plurality of transmitting/receiving antennas. In MIMO transmission, different signals are transmitted from a plurality of transmitting antennas at the same frequency, at the same time, and the receiving side receives spatial-multiplexed signals by demultiplexing the signals through signal processing. One such example of signal demultiplexing scheme is a parallel interference canceller (e.g. Non-Patent Document 1). A parallel interference canceller generates a replica signal first by demultiplexing and demodulating signals and then re-modulating the result. Next, interference signals are canceled from the received signal using the replica signal generated. The signal is then re-demodulated and received data is obtained. Thus, reception performance can be improved by repeating re-modulation and re-demodulation.
Conventionally, as a method of reducing the reception delay of an OFDM (Orthogonal Frequency Division Multiplexing) signal in such circumstances, there is a method of combining into one the data rearrangement processes that are carried out in a plurality of locations in the OFDM receiving apparatus (e.g. Patent Document 1). The data rearrangement processes are carried out through interleaving and deinterleaving. In order to rearrange data in this case, given that data normally needs to be cumulated in units of a certain amount, processing delay is produced.
FIG. 1 shows main reception process delays in a parallel interference canceller using OFDM modulation. In FIG. 1, the vertical axis shows various processes to be sequentially applied to received data, and the horizontal axis shows elapsed time. Furthermore, the rectangles in FIG. 1 denote data output units as results of various processes. Each rectangle in this case expresses data of one OFDM symbol, which is the unit when performing FFT (Fast Fourier Transfer) processing. In FIG. 1, received signal 10-0 is subjected to FFT processing after the FFT processing delay 10-1. Data 10-2 after the FFT processing is outputted. As shown in Patent Document 1, since the FFT processing requires data to be cumulated in units of FFT processing, processing delay 10-1 is generated.
Next, the data subjected to the FFT processing is subjected to deinterleaving processing. Deinterleaving requires data to be cumulated for rearrangement, and therefore deinterleaved data 10-4 is outputted deinterleaving processing delay 10-3 later. The deinterleaved data is then subjected to error correction decoding and error-corrected data 10-6 is outputted after error correction decoding processing delay 10-5.
Next, the parallel interference canceller performs re-modulation processing to cancel an interference signal. In this case, the error-corrected data is interleaved for re-modulation. In the interleaving processing, error-corrected data is received as input and interleaved data 10-8 is outputted after interleaving processing delay 10-7. In this case, since data to be rearranged is stored once as in the case of interleaving processing and deinterleaving processing, processing delay 10-7 is generated. Interference of the interleaved data is canceled through canceller processing and data 10-10 with interference canceled is outputted after canceller processing delay 10-9. The canceled signal is subjected to rearrangement processing through deinterleaving and deinterleaved data 10-12 is outputted after deinterleaving processing delay 10-11. The deinterleaved data is subjected to error correction decoding through error correction decoding and decoded data 10-14 is outputted after error correction decoding processing delay 10-13.    Non-Patent Document 1: Koji Shibahara, et al. “Performance Evaluation of Parallel Interference Canceller for FEC-coded. MIMO-SDM,” Proceedings of the 2004 IEICE General Conference, B-5-32, 2004    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-60614